The present invention relates to hydraulic systems having a pump that supply pressurized fluid to one or more actuators that operate devices on machinery, and particularly to recovering energy produced from lowering loads and stopping inertial loads in such systems.
Construction and agricultural equipment have moveable members which are operated by an actuator, such as a hydraulic cylinder and piston arrangement. Application of pressurized hydraulic fluid from a pump to the actuator can be controlled by a set of proportional solenoid valves of a type described in U.S. Pat. No. 5,878,647. When an operator desires to move a member on the equipment a control lever is operated to send signals to the solenoid valves for the cylinder associated with that member. One solenoid valve is opened to supply pressurized fluid to the cylinder chamber one side of the piston and another solenoid valve opens to allow fluid being forced from the opposite cylinder chamber to drain to a reservoir, or tank. By varying the degree to which the solenoid valves are opened, the rate of flow into the associated cylinder chamber can be varied, thereby moving the piston at proportionally different speeds.
Many hydraulic systems waste energy by lowering loads (potential energy) or by stopping inertial loads (kinetic energy) through dissipation devices, such as restrictive valving or friction braking.
Some prior hydraulic systems direct the fluid forced from the non-powered cylinder chamber to assist in powering the other chamber of the same cylinder, rather than routing the expelled fluid to the tank. This enables the piston of that cylinder to move at a faster speed that the pressure from the pump would otherwise enable. This action, reduces the cycle time of the hydraulic actuator. Recycling the hydraulic fluid from a non-powered chamber to the powered chamber of the same cylinder often is referred to in the art as xe2x80x9cregenerationxe2x80x9d.
The present invention relates to recovering the potential and kinetic energy produced in a hydraulic system by the loads. This recovered energy is used to operate another simultaneous commanded actuator function, store energy in an accumulator, or add torque to the prime mover.
A regeneration method for a hydraulic system utilizes hydraulic fluid drained under pressure from an actuator in the system, as occurs due to the force of a load acting on the actuator. The pressure of the hydraulic fluid being drained from the actuator is sensed to produce an indication of a first pressure. The pressure of hydraulic fluid at an inlet of a hydraulic power converting device in the system also is sensed to produce an indication of a second pressure. When the first pressure is greater than the second pressure, the drained hydraulic fluid is routed to the inlet of the hydraulic power converting device to drive the latter device.
The hydraulic power converting device may be another actuator or the pump of the hydraulic system where the pump is configured to act as a motor and drive the prime mover. As an alternative, the fluid drained from the actuator is stored under pressure in an accumulator. Thereafter when hydraulic power is required by an actuator, the fluid is routed from the accumulator to that actuator requiring power.
A unique hydraulic system also is described for implementing this method. The system has a transfer line through which the hydraulic fluid drained from an actuator is routed as an alternative to sending that fluid to the system tank. Check valves enable the one-way flow of fluid from the draining actuator to the transfer line. Isolation valves connect the transfer line to the inlet of conventional control valves that regulate the supply of fluid from the pump to the actuators. Proportional regeneration regulation valves control the flow of fluid from the draining actuator to the tank so that at least a portion of that fluid will be directed to the transfer line. By selectively controlling the isolation and regeneration regulation valves, the fluid draining from one actuator can be used to power another actuator. Other variations of the regeneration system enable the draining fluid to drive the pump as a motor, thereby driving the prime mover attached to the pump.